Radio-frequency identification (RFID) is a technology that uses communication via radio waves to exchange data between a reader and an electronic tag attached to an object, for the purpose from identification to tracking. Generally, a radio-frequency identification system involves RFID readers, RFID tags, and an application system. It is noted that the RFID system can be designed to operate using different radio frequencies under different regulations, the operating frequencies include low-frequency (LF) at 134 KHz typically, high-frequency (HF) at 13.56 MHz, ultra-high-frequency (UHF) at 860˜960 MHz, and microwave at 2.4 GHz, and so on. The passive RFID tags have no power source internally and require an external electromagnetic field, that is mostly emitted from RFID readers, to power and activate an internal analog circuit embedded in the passive RFID tags for the chip operations. Generally, such an RFID tag can be embedded with memories for data storage, and the memories can be read-only memories (ROM), write-once-read-many (WORM) memories or electrically erasable programmable read-only memories (EEPROM). Since the passive RFID tags and readers utilize the electromagnetic waves to transfer energy and signals, and their signal transmission performance, especially the frequency response of the RFID tags' antennas, can easily be affected by the material characteristics of the objects on which the RFID tags are attached, or even by the metallic objects as well as the conductive materials that are located neighboring thereto. That is, the metallic objects as well as the conductive materials, whichever are distributed neighboring to an RFID tags, will cause an interference phenomenon to be generated by a degree depending on the volume/area of those conductive materials and also the distances there between, that will affect the reading performance of the RFID system. Moreover, since the electromagnetic waves used for signal transmission in the RFID system are invisible waves, neither the constructive interference nor the destructive interference caused by those surrounding metallic objects or conductive materials are not perceptible. Consequently, it can be a very time consuming job just to determine where and how to attach a passive RFID tag on an object in those conventional RFID systems, since it is simply a try-and-error task that the passive RFID tag usually will have to be attached to the object again and again at different positions for obtaining different read rates accordingly so as to be used as base for locating a most appropriate position on the object for the RFID tag to attach thereto.
Generally, in a conventional RFID system, whether an RFID tag is fabricated with good quality for enabling the same to function normally, or whether the RFID tag is placed at an appropriate location or simply being placed properly can be determined according to its received signal strength indication (RSSI) or its read rate, and in a situation when the RSSI is weak or the read rate is poor while it is assured that the RFID tag is not working properly, it can be determined that the RFID tag is not located correctly and should be moved to other position. However, a common RFID tag is not built to be attached to and detached from an object repetitively in the abovementioned try-and-error manner so as to be placed properly that the RFID tag can be damaged during the repetitive processes, and moreover, such repetitive attaching and detaching will wear down the adhesion of the RFID tag, and thus the RFID tag might lose accidently and unintentionally even after being positioned properly. Nevertheless, no matter the RFID tag is damaged during the repetitive processes or is moved accidentally and unintentionally even after being positioned properly, there is a conceivable waste in resource, time and manpower already.